Experimental evidence indicates that the efficacy of photodynamic therapy (PDT) is temperature-dependent. This insight creates the possibility of using a temperature gradient in the tissue to compensate partially for the rapid attenuation of light, thus allowing effective treatment to a greater depth. By pulsing the surface temperature at an appropriate rate and illuminating only during the cool phase, the treatment will occur at a selected depth during the warm phase, due to the propagation delay experienced by the temperature wave.